A conventional gas turbine engine includes a compressor, a combustor and a turbine. The compressor compresses ambient air which is supplied to the combustor where the compressed air is combined with a fuel and ignites the mixture, creating combustion products defining a working gas. The working gas is supplied to the turbine where the gas passes through a plurality of paired rows of stationary vanes and rotating blades. The rotating blades are coupled to a shaft and disc assembly. As the working gas expands through the turbine, the working gas causes the blades, and therefore the shaft and disc assembly, to rotate.
Combustors often operate at high temperatures that may exceed 2,500 degrees Fahrenheit. Typical turbine combustor configurations expose turbine blade assemblies to these high temperatures. As a result, turbine blades must be made of materials capable of withstanding such high temperatures. In addition, turbine blades often contain cooling systems for prolonging the life of the blades and reducing the likelihood of failure as a result of excessive temperatures.
Typically, turbine blades comprise a root, a platform and an airfoil that extends outwardly from the platform. The airfoil is ordinarily composed of a tip, leading edge and a trailing edge. Most blades typically contain internal cooling channels forming a cooling system. The cooling channels in the blades may receive air from the compressor of the turbine engine and pass the air through the blade. The cooling channels often include multiple flow paths that are designed to maintain the turbine blade at a relatively uniform temperature. However, centrifugal forces and air flow at boundary layers often prevent some areas of the turbine blade from being adequately cooled, which results in the formation of localized hot spots. Localized hot spots, depending on their location, can reduce the useful life of a turbine blade and can damage a turbine blade to an extent necessitating replacement of the blade.
Operation of a turbine engine results in high stresses being generated in numerous areas of a turbine blade. One particular area of high stress is found in the blade's trailing edge, which is a portion of the blade forming a relatively thin edge that is generally orthogonal to the flow of gases past the blade and is on the downstream side of the blade. Because the trailing edge is relatively thin and an area prone to development of high stresses during operation, the trailing edge is highly susceptible to formation of cracks. These cracks may propagate and cause failure of the blade, which may, in some situations, cause catastrophic damage to a turbine engine.
A conventional cooling system in a turbine blade assembly may discharge a substantial portion of the cooling air through a trailing edge of the blade. Typically, the cooling system contains an intricate maze of cooling flow paths in the trailing edge. There exist numerous configurations of the cooling flow paths that attempt to maximize the convection occurring in a trailing edge of a blade. While many of these conventional systems have operated successfully, a need still exists to provide increased cooling capability in the trailing edge portions of turbine blades.